“With so many consumers using mobile phones rather than landlines to contact essential services, find information and seek help, it is more important than ever that they do so for free across all 0800 numbers.”

The move follows BT's recent announcement that all landline calls to 0870 and 0845 numbers would be free to its customers.

Peter Morris, BT director of consumer and corporate services said the move was in response to growing discontent among hard-pressed consumers.

“We think mobile customers are irritated by having to pay high rates to call ‘free’ 0800 numbers, so we have put our own house in order by making it free for any BT Mobile customer to call these numbers,” he said.

“We have all called an 0800 number from our mobiles and experienced the frustration of the message telling us that the call will be charged at standard rates.

“We had already made calls into BT free for our 14m landline customers and we are happy to back Consumer Focus and other consumer organisations in their efforts to address this anomaly.”